Analysis of the long range α-particles from radium C' by the magnetic focussing method

In our last paper we gave an account of an annular ring magnet capable of focussing groups ofα -particles after they have traversed a semicircle of 40 cm. radius. By this method the velocities of a number of important groups ofα -particles were measured with a relative accuracy, it is believed, of 1 in 5000. Preliminary measurements were described of the two long range groups from thorium C´ and of two from radium C´. In a previous paper we had shown by means of counting methods that the long range groups ofα -particles from radium C´ were much more complicated than those from thorium C´, and consisted of at least nine distinct groups. This older method, however, had not sufficient resolving power to separate completely a number of these groups, and the annular ring magnet was constructed primarily to make a more complete analysis of thisα -ray spectrum. It is hardly necessary at this stage to emphasize the importance of accurate measurements of the energies of these groups, for they give us direct information of the energy levels of theα -particle in an excited nucleus, which is of fundamental importance in considering the question of the origin of theγ -rays from radium C´.